Systems and techniques for channel gain computations

ABSTRACT

Systems and techniques for controlling transmission power involve receiving a first to second channel power ratio, receiving a first to second channel power ratio, adjusting the power ratio if a combined power of a plurality of channels exceeds a threshold, the channels including the first and second channels, and computing gain of the first channel as a function of the power ratio. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or the meaning of the claims.

CROSS REFERENCE

This application claims priority from Provisional Application No.60/340,512, filed Dec. 14, 2001, entitled “Systems and Techniques forChannel Gain Computations” and is assigned to the assignee of thepresent application.

BACKGROUND

1. Field

The present invention relates to communications systems, and morespecifically, to systems and techniques for controlling transmissionpower in a wireless communications system.

2. Background

Modern communications systems are designed to allow multiple users toaccess a common communications medium. Numerous multiple-accesstechniques are known in the art, such as time division multiple-access(TDMA), frequency division multiple-access (FDMA), space divisionmultiple-access, polarization division multiple-access, code divisionmultiple-access (CDMA), and other similar multi-access techniques. Themultiple-access concept is a channel allocation methodology which allowsmultiple user access to a common communications link. The channelallocations can take on various forms depending on the specificmulti-access technique. By way of example, in FDMA systems, the totalfrequency spectrum is divided into a number of smaller sub-bands andeach user is given its own sub-band to access the communications link.Alternatively, in TDMA systems, each user is given the entire frequencyspectrum during periodically recurring time slots. In CDMA systems, eachuser is given the entire frequency spectrum for all of the time butdistinguishes its transmission through the use of a code.

In multi-access communications systems, techniques to reduce mutualinterference between multiple users are often utilized to increase usercapacity. By way of example, power control techniques can be employed tolimit the transmission power of each user to that necessary to achieve adesired quality of service. This approach ensures that each usertransmits only the minimum power necessary, but no higher, therebymaking the smallest possible contribution to the total noise seen byother users. These power control techniques may become more complex inmulti-access communications systems supporting users with multiplechannel capability. In addition to limiting the transmission power ofthe user, the allocated power should be balanced between the multiplechannels in a way that optimizes performance.

SUMMARY

In one aspect of the present invention, a method of controllingtransmission power includes receiving a first to second channel powerratio, adjusting the power ratio if a combined power of a plurality ofchannels exceeds a threshold, the channels including the first andsecond channels, and computing gain of the first channel as a functionof the power ratio.

In another aspect of the present invention, a computer readable mediaembodying a method of controlling transmission receives a first tosecond power ratio, adjusts the power ratio if a combined power of aplurality of channels exceeds a threshold, the channels including thefirst and second channels, and computes gain of the first channel as afunction of the power ratio.

In yet another aspect of the invention, an apparatus including atransmitter gain control configured to receive a first to second channelpower ratio, adjust the power ratio if a combined power of a pluralityof channels exceeds a threshold, the channels including the first andsecond channels, compute gain of the first channel as a function of thepower ratio, and a transmitter configured to apply the computed gain tothe first channel, combine the channels, and apply a second gain to thecombined channels.

In a further aspect of the present invention, an apparatus includesmeans for receiving a first to second power ratio, means for adjustingthe power ratio if a combined power of a plurality of channels exceeds athreshold, the channels including the first and second channels, andmeans for computing gain of the first channel as a function of the powerratio.

It is understood that other aspects of the present invention will becomereadily apparent to those skilled in the art from the following detaileddescription, wherein is shown and described only exemplary embodimentsof the invention, simply by way of illustration. As will be realized,the invention is capable of other and different embodiments, and itsseveral details are capable of modifications in various respects, allwithout departing from the invention. Accordingly, the drawings anddescription are to be regarded as illustrative in nature, and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present invention are illustrated by way of example, andnot by way of limitation, in the accompanying drawings in which likereference numerals refer to similar elements:

FIG. 1 is a simplified functional block diagram of an exemplary CDMAcommunications system;

FIG. 2 is a functional block diagram of an exemplary subscriber stationadapted for operation in a CDMA communications system;

FIG. 3 is a functional block diagram an exemplary transmitter gaincontrol and transmitter from the subscriber station of FIG. 2;

FIG. 4 is a flow chart illustrating an exemplary back off algorithmimplemented by the transmitter gain control of FIG. 3; and

FIG. 5 is a flow chart illustrating an alternative exemplary back offalgorithm implemented by the transmitter gain control of FIG. 3.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of thepresent invention and is not intended to represent the only embodimentsin which the present invention can be practiced. The term “exemplary”used throughout this description means “serving as an example, instance,or illustration,” and should not necessarily be construed as preferredor advantageous over other embodiments. The detailed descriptionincludes specific details for the purpose of providing a thoroughunderstanding of the present invention. However, it will be apparent tothose skilled in the art that the present invention may be practicedwithout these specific details. In some instances, well known structuresand devices are shown in block diagram form in order to avoid obscuringthe concepts of the present invention.

In an exemplary embodiment of a communications system, a power controlsystem can be used to increase the number of users that can be supportedby the system. For those users with multi-channel capability, gaincomputation techniques can be employed to balance the relativetransmission power between the channels. The gain computations can beperformed through a power estimation process which controls thetransmission power for one or more channels. In the event that the totaltransmission power exceeds the power limitations of the user, asystematic back off procedure can be used to reduce the gain of one ormore channels.

Various aspects of these gain computation techniques will be describedin the context of a CDMA communications system, however, those skilledin the art will appreciate that the techniques for gain computation ofmultiple channels are likewise suitable for use in various othercommunications environments. Accordingly, any reference to a CDMAcommunications system is intended only to illustrate the inventiveaspects of the present invention, with the understanding that suchinventive aspects have a wide range of applications.

CDMA is a modulation and multiple access scheme based on spread-spectrumcommunications. In a CDMA communications system, a large number ofsignals share the same frequency spectrum and, as a result, provide anincrease in user capacity. This is achieved by transmitting each signalwith a different pseudo-random noise (PN) code that modulates a carrier,and thereby, spreads the spectrum of the signal waveform. Thetransmitted signals are separated in the receiver by a correlator thatuses a corresponding PN code to despread the desired signal=s spectrum.The undesired signals, whose PN codes do not match, are not despread inbandwidth and contribute only to noise.

FIG. 1 is a simplified functional block diagram of an exemplary CDMAcommunications system. A base station controller 102 can be used toprovide an interface between a network 104 and all base stationsdispersed throughout a geographic region. For ease of explanation, onlyone base station 106 is shown. The geographic region is generallysubdivided into smaller regions known as cells. Each base station isconfigured to serve all subscriber stations in its respective cell. Insome high traffic applications, the cell may be divided into sectorswith a base station serving each sector. In the described exemplaryembodiment, three subscriber stations 108 a-c are shown in communicationwith the base station 106. Each subscriber station 108 a-c may accessthe network, or communicate with other subscriber stations, through oneor base stations under control of the base station controller 102.

A power control system can be employed to reduce mutual interferencebetween the multiple subscriber stations. The power control system canbe used to limit the transmission power over both the forward andreverse links to that necessary to achieve a desired quality of service.The forward link refers to transmissions from the base station to asubscriber station, and the reverse link refers to transmissions from asubscriber station to the base station. For the purposes ofillustration, the gain computation techniques will be described withreference to the reverse link, however, as those skilled in the art willreadily appreciate, these gain computation techniques are equallyapplicable to the forward link.

The reverse link transmission power is typically controlled with twopower control loops. The first power control loop is an open loopcontrol. The open control loop is designed to control the reverse linktransmission power as a function of path loss, the effect of basestation loading, and environmentally induced phenomena such as fastfading and shadowing. This open control loop estimation process is wellknown in CDMA communications systems.

The second power control loop is a closed loop control. The closed loopcontrol has the function of correcting the open loop estimate toachieved a desired signal-to-noise ratio (SNR) at the base station. Thiscan be achieved by measuring the reverse link transmission power at thebase station and providing feedback to the subscriber station to adjustthe reverse link transmission power. The feedback signal can be in theform of a reverse power control (RPC) command which is generated bycomparing the measured reverse link transmission power at the basestation with a power control set point. If the measured reverse linktransmission power is below the set point, then an RPC up command isprovided to the subscriber station to increase the reverse linktransmission power. If the measured reverse link transmission power isabove the set point, then an RPC down command is provided to thesubscriber station to decrease the reverse link transmission power.

The open and closed loop controls may be used to control thetransmission power of various reverse link channel structures. By way ofexample, in some CDMA communications systems, the reverse link waveformincludes a traffic channel to carry voice and data services to the basestation and a pilot channel used by the base station for coherentdemodulation of the voice and data. In these systems, the open andclosed loop controls can be used to control the reverse link power ofthe pilot channel. In order to optimize performance, the power of thepilot channel can then be balanced with the power of the trafficchannel. Specifically, each channel can be spread with a uniqueorthogonal code generated by using Walsh functions. A gain can thenapplied to the traffic channel in order to maintain an optimal trafficto pilot channel power ratio.

This principle can be extended to additional channels in the reverselink waveform. In CDMA communications systems with a variable data rate,for example, a data rate control (DRC) channel containing a DRC messageis generally supported by the reverse link transmission. In the variabledata rate mode, the data rate of the forward link transmission isdictated by the DRC message. The DRC message is typically based on acarrier-to-interference (C/I) estimation performed at the subscriberstation. This approach provides a mechanism for the base station toefficiently transmit the forward link data at the highest possible rate.An exemplary CDMA communications system supporting a variable data raterequest scheme is a High Data Rate (HDR) communications system. The HDRcommunications system is typically designed to conform one or morestandards such as the “cdma2000 High Rate Packet Data Air InterfaceSpecification,” 3GPP2 C.S0024, Version 2, Oct. 27, 2000, promulgated bya consortium called “3^(rd) Generation Partnership Project,” thecontents of the aforementioned standard being incorporated by referenceherein.

In the described exemplary HDR communications system, the reverse linktransmission may also support an acknowledgment (ACK) channel. The ACKchannel is used to indicate to the base station that the subscriberstation has successfully decoded a packet received over the forwardlink. This can be achieved by sending an ACK message over the ACKchannel.

In these HDR communications systems, the power of the pilot channel canalso be balanced with the power of the DRC and ACK channels. Thisprocess involves spreading each of the DRC and ACK channels with aunique orthogonal code generated by using Walsh functions. A DRC gaincan then be applied to the DRC channel to maintain an optimal DRC topilot channel power ratio. Similarly, an ACK gain can also be applied tothe ACK channel to maintain an optimal ACK to pilot channel power ratio.

A functional block diagram of an exemplary subscriber station operatingin an HDR communications system is shown in FIG. 2. The exemplarysubscriber station includes a receiver and a transmitter both coupled toan antenna 202. The receiver includes an RF front end 204, a demodulator206 and a decoder 208. The transmitter includes an encoder 209, amodulator 210, and shares the RF front end 204 with the receiver. Thetransmitter also includes a transmitter gain control 214 to control thereverse link transmission power in a manner to be discussed in greaterdetail later.

The RF front end 204 is coupled to the antenna 202. The receiver portionof the front end 204 downconverts, filters, amplifies and digitizes asignal received by the antenna 202. The receiver portion of the RF frontend 204 also includes an AGC (not shown) to maximize the dynamic rangeof the digitized signal. The AGC can be utilized by the transmitter gaincontrol 214 to compute the path loss between the base station and thesubscriber station during the open loop power control estimation. Thedigitized signal from the receiver portion of the RF front end 204 canthen be coupled to the demodulator 206 where it is quadraturedemodulated with short PN codes, decovered by Walsh codes, anddescrambled using a long PN code. The demodulated signal can then beprovided to the decoder 208 for forward error correction. Thedemodulator 206 can also be used to extract the RPC command from thereverse link transmission and provide it to the transmitter gain control214 for closed loop power control computations.

The transmitter includes the encoder 209 which typically providesconvolution coding and interleaving of the reverse link traffic channel.The encoded traffic channel is provided to the modulator 210 where it isspread with a Walsh cover and amplified by a traffic channel gain(G_(T)) computed by the transmitter gain control 214. The pilot channel,DRC channel, and ACK channel are also provided to the modulator 210where they are each spread with a different Walsh cover and amplified byrespective channel gains (G_(P)), (G_(D)), and (G_(A)) computed by thetransmitter gain control 214. The channels are then combined, spreadwith a long PN code and quadrature modulated with short PN codes. Thequadrature modulated signal is provided to the transmitter portion ofthe RF front end 204 where it is upconverted, filtered, and amplifiedfor over the air forward link transmission through the antenna 202. Theamplification of the quadrature modulated signal in the transmitterportion of the RF front end 204 is controlled by an AGC signal from thetransmitter gain control 214.

A functional block diagram of an exemplary transmitter gain control 214,modulator 210 and transmitter portion of the RF front end 204 is shownin FIG. 3. The transmitter gain control 214 includes a power and gaincomputation block 302 for computing the gains for the pilot, traffic,DRC, and ACK channels. The gain computations are based on predeterminedpower ratios for the traffic, DRC and ACK channels with respect to thepilot channel. A feedback loop can be used to reduce the channel gainsunder power limiting conditions by “throttling” or “backing off” thepredetermined power ratios for the DRC and ACK channels. The feedbackloop includes a limiter 304 and a power throttle block 306. The limiter304 determines whether the total reverse link transmission powerresulting from the predetermined power ratios exceeds the maximum powercapability of the transmitter. The maximum power capability of thetransmitter is limited by a variable gain amplifier (VGA) 308 and apower amplifier (not shown) in the RF front end 204. In the describedexemplary embodiment, the power and gain computation block 302 alsocomputes the total reverse link transmission power based on thepredetermined power ratios and the estimated reverse link power for thepilot channel. If the resultant total reverse link transmission powerexceeds the power capability of the transmitter, the power throttleblock 306 is used to back off the power ratios for the DRC and ACKchannels in a manner to be described in greater detail later.

The transmitter gain control 214 can be implemented with a variety oftechnologies including, by way of example, embedded communicationssoftware. The embedded communications software can be run on aprogrammable digital signal processor (DSP). Alternatively, thetransmitter gain control 214 can be implemented with a general purposeprocessor running a software program, an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof.

In the described exemplary embodiment, the power ratios for the traffic,DRC and ACK channels with respect to the pilot channel can be used tocompute the channel gains. Accordingly, computational complexity can bereduced if the appropriate power ratios are first determined using thefeedback loop before the gain computations are made. As explained above,the feedback loop is used to “throttle” or “back off” the predeterminedpower ratios of the DRC and ACK channels with respect to the pilotchannel if the total reverse link transmission power exceeds the maximumpower capability of the transmitter. The total reverse link transmissionpower can be computed by solving the following equation:

Total Power=Pilot Channel Power+10 log₁₀ (1+P _(T)+β_(D) ·P _(D)+β_(A)·P _(A))  (1)

where:

P_(T) is the traffic to pilot channel power ratio;

P_(D) is the DRC to pilot channel power ratio;

β_(D) is a value used to back off the DRC power ratio;

P_(A) is the ACK to pilot channel power ratio; and

β_(A) is a value used to back off the ACK power ratio.

The “Pilot Chanel Power” is estimated by two power control loops. Anopen loop control 310 generates an estimate of the required transmissionpower on the pilot channel based on the average value of the AGC fromthe receiver. The open loop estimate can then be computed by means wellknown in the art for nominal base station loading and Effective RadiatedPower (ERP). Information about variations from the nominal base stationloading and ERP can be communicated from the base station to thesubscriber station and used to adjust the open loop estimate by meanswell known in the art.

A closed loop control 312 can be used to increment or decrement thecurrent closed loop estimate based on the RPC commands recovered fromthe demodulator. The resultant closed loop estimate is summed with theopen loop estimate by a summer 314. The sum of the open and closed loopestimates yields the total reverse link power for the pilot channel.This sum is provided to the power and gain computation block 302 whereit is used as the “Pilot Channel Power” in equation (1).

The traffic to pilot channel power ratio P_(T) can be computed in avariety of fashions. In at least one embodiment, the traffic to pilotchannel power ratio can be predetermined for each data rate supported bythe reverse link transmission either by empirical analysis, simulation,experimentation, or any other means to achieve a desired quality ofservice. By way of example, in at least one simulation it has been shownthat for a 9.6 k data rate, the traffic to pilot channel ratio should bebetween −2.25 db and 9 dB. If the data rate is increased to 38.4 k, thetraffic to pilot channel power ratio should be between 3.75 dB and 15dB. Those skilled in the art will readily be able to determine theappropriate traffic to pilot channel power ratio values for all datarates supported by their particular application. These predeterminedpower ratio values can be stored at the base station and transmitted toeach subscriber station in its respective cell or sector over a forwardlink control channel. Alternatively, the predetermined power ratiovalues can be stored or computed at the subscriber station.

The DRC to pilot channel power ratio P_(D) and the ACK to pilot channelratio P_(A) can also be computed in a variety of fashions. Similar tothe traffic to pilot channel power ratio, the DRC and ACK power ratioscan be predetermined either by empirical analysis, simulation,experimentation, or any other means to achieve a desired quality ofservice. In at least one embodiment of the exemplary HDR communicationssystem, the DRC to pilot channel power ratio can take on values between−9 dB and 6 dB in 1 dB increments and the ACK to pilot channel powerratio can take on values between −3 dB and 6 dB also in 1 dB increments.These predetermined power ratio values can be stored at the base stationand transmitted to each subscriber station in its respective cell orsector over the control channel. Alternatively, the predetermined powerratio values can be stored or computed at the subscriber station.

To compute the total reverse link transmission power from equation (1),the channel power ratio values can be converted into the linear domainas follows:

P _(T)=10^((Traffic Power Ratio Value/10))  (2)

P _(D)=10^((DRC Power Ratio Value/10))  (3)

 P _(A)=10^((ACK Power Ratio Value/10))  (4)

The power throttle block 306 is used to reduce the power ratios for theDRC and ACK channels under power limiting conditions. The power throttleblock 306 can accomplish this by generating values β_(D) and β_(A) andfeeding them back to the power and gain computation block 302 forscaling the DRC and ACK power ratios, respectively. The DRC and ACKvalues can be expressed in the linear domain respectively as:

β_(D)=10^((−DRCbackoff/10))  (5)

β_(A)=10^((−ACKbackoff/10))  (6)

From the above equations, one skilled in the art will readily appreciatethat a 1 dB reduction in the DRC to pilot channel power ratio can beachieved by setting “DRCbackoff” in equation (5) to 1. A 2 dB reductionin the ACK to pilot channel power ratio can be achieved by setting“ACKbackoff” in equation (6) to 2. Thus, any incremental reductionscheme can be implemented depending on the particular design parametersand the specific communications application.

In the described exemplary embodiment, the “Total Power” in equation (1)is initially computed by the power and gain computation block 302 withthe values β_(D) and β_(A) set to 1 so that the power ratios for eachchannel are set to their predetermined optimal or desired values. Thecomputed “Total Power” is provided to the limiter 304. The limiter 304compares the computed “Total Power” to the maximum power capability ofthe transmitter. If the computed “Total Power” exceeds the powerlimitations of the transmitter, then the reverse link data rate can belowered to reduce the total reverse link transmission power. In responseto the reduced data rate, the power and gain computation block 302selects a new predetermined traffic to pilot channel power ratiocorresponding to the reduced data rate. The “Total Power” can then berecomputed by the power and gain computation block 302 and provided tothe limiter 304 for comparison with the maximum power capability of thetransmitter. This procedure continues until the computed “Total Power”comes within the power capability of the transmitter or the reverse linkdata rate is reduced to the lowest data rate supported by thecommunications system.

In the event that the “Total Power” computed by the power and gaincomputation block 302 exceeds the maximum power capability of thetransmitter at the lowest data rate supported by the communicationssystem, the limiter 304 can be used to ratchet the closed loop control312 such that RPC up commands are ignored. This can be achieved byholding the current closed loop estimate constant in response to an RPCup command and reducing the current closed loop estimate in response toan RPC down command. In some embodiments, ratcheting can be supported atboth ends of the transmitter power level such that RPC down commands areignored if the reverse link transmission power is below a minimumoperating threshold.

The limiter 304 also enables the power throttle block 306 to implement a“back off” algorithm to adjust the values β_(D) and β_(A) tosystematically reduce the power ratios for one or both of the DRC andACK channels until the “Total Power” computed by the power and gaincomputation block is within the maximum power capability of thetransmitter. The manner in which the values β_(D) and β_(A) are reducedand the resultant incremental reduction in the power ratios of thechannels may vary depending on the system application and the overalldesign constraints.

A flow chart illustrating an exemplary back off algorithm is shown inFIG. 4. Initially, the limiter is used to enable the back off algorithmin step 402. Once the back off algorithm is enabled, a DRC power loop404 is entered into. In the DRC power loop 404, the DRC to pilot channelpower ratio can backed off by 1 dB in step 406. This can be achieved byrecomputing the DRC value β_(D) with the “DRCbackoff” in equation (5)at 1. Alternatively, the “DRCbackoff” in equation (5) can be set to anyvalue to achieve a desired reduction in the DRC to pilot channel powerratio. In any event, the recomputed DRC value β_(D) can be fed back tothe to the power and gain computation block. The “Total Power” can thenbe recomputed and provided to the limiter to determine whether the totalreverse link transmission power is within the maximum power capabilityof the transmitter.

In step 408, the results from the limiter are provided to the gainthrottle block. If the recomputed “Total Power” is within the maximumpower capability of the transmitter, the power throttle block isdisabled in step 410. Conversely, if the recomputed “Total Power” stillexceeds the maximum power capability of the transmitter, then the powerthrottle block determines whether the DRC channel remains in the “on”state in step 412. The DRC channel is determined to be in the “on” stateit the DRC β_(D) is greater than 0, or some other minimum thresholdvalue. If the DRC channel remains in the “on” state, then the algorithmloops back to step 406 and reduces the DRC to pilot channel power ratioanother dB by setting the “DRCbackoff” in equation (5) to 2 which willresult in a 2 dB reduction in the DRC to pilot channel ratio. The backoff algorithm remains in the DRC power loop 404 until either the powerthrottle block is disabled in step 410 or the DRC value β_(D) is reducedbelow the minimum threshold. Should the DRC value β_(D) be reduced belowthe minimum threshold, then the back off algorithm exits the DRC powergain loop 404 and enters an ACK power loop 416.

In the ACK power loop 416, the ACK to pilot channel power ratio canbacked off by 1 dB in step 418. This can be achieved by recomputing theACK value β_(A) with the “ACKbackoff” in equation (6) at 1.Alternatively, the “ACKbackoff” in equation (6) can be set to any valueto achieve a desired reduction in the ACK to pilot channel power ratio.In any event, the recomputed ACK value β_(A) can be fed back to the tothe power and gain computation block. The “Total Power” can then berecomputed and provided to the limiter 304 to determine whether thetotal reverse link transmission power is within the maximum powercapability of the transmitter.

In step 420, the results from the limiter are provided to the gainthrottle block. If the recomputed “Total Power” is within the maximumpower capability of the transmitter, the power throttle block isdisabled in step 424. Conversely, if the recomputed “Total Power” stillexceeds the maximum power capability of the transmitter, then the powerthrottle block determines whether the ACK channel remains in the “on”state. The ACK channel is determined to be in the “on” state if the ACKvalue β_(A) is greater than 0, or some other minimum threshold value. Ifthe ACK channel remains in the “on” state, then the algorithm loops backto step 418 and reduces the ACK to pilot channel power ratio another dBby setting the “ACKbackoff” in equation (6) to 2 which will result in a2 dB reduction in the ACK to pilot channel ratio. The back off algorithmremains in the ACK power loop 416 until either the power throttle blockis disabled by the limiter in step 424 or the ACK value β_(A) is reducedbelow the minimum threshold. Should the ACK value β_(A) be reduced belowthe minimum threshold, then the back off algorithm is disabled byexiting the ACK power loop in step 424. In that event, other powerreduction techniques can be employed to bring the total reverse linktransmission power within the maximum power capability of thetransmitter.

The exemplary embodiment of the back off algorithm described inconnection with FIG. 4 may be computationally intensive depending on thepredetermined power ratios for the DRC and ACK channels. By way ofexample, if the predetermined power ratios for the DRC and ACK channelsare each set to the 6 dB maximum, there is a possibility that 16 passesthrough the DRC power loop and 10 passes through the ACK power loopmight be required to back off the DRC and ACK power ratios. To reducethe potential computational complexity, an alternative back offalgorithm may be implemented that computes the DRC value β_(D) in asingle step, and if necessary, computes the ACK value β_(A) in a singlestep. This can be achieved in a variety of ways. By way of example,equation (1) can be manipulated to solve for the value of interest bydefining a total power to pilot channel power ratio and setting it to avalue relating to the maximum power capability of the transmitter. Thiscan be achieved by rewriting equation (1) in the linear domain as:

R=1+P _(T) +P _(D) +P _(A)  (7)

R _(M)≧1+P _(T)+β_(D) ·P _(D)+β_(A) ·P _(A)  (8)

where R represents the total power to pilot channel power ratio beforeenabling the back off algorithm, and R_(M) is the maximum allowed valueof R after computing the values β_(D) and β_(A).

A flow chart illustrating an exemplary algorithm utilizing equations (7)and (8) is shown in FIG. 5. In step 502, the total power to pilotchannel power ratio R is computed. The computed power ratio is thencompared to the maximum allowable total power to pilot channel powerratio R_(M) in step 504. If R≦R_(M), then the DRC and ACK power ratiosdo not require back off. In that event, the values β_(D) and β_(A) areset to 1 by the power throttle block and fed back to the power and gaincomputation block in step 506. Conversely, if R is greater than R_(M),the DRC value β_(D) can then be computed in step 508.

The DRC value β_(D) can be computed by setting the ACK value β_(A) to 1and solving for the DRC value β_(D) in equation (8). With the ACK valueβ_(A) set to 1, equation (8) can be rewritten as:

β_(D)=(R _(M)−1−P _(T) −P _(A))/P _(D)  (9).

In step 510, the resultant DRC value computation is examined todetermine whether it is positive. If β_(D)≧0, then the computed DRCvalue β_(D) will reduce the DRC to pilot channel power ratio to a levelthat will result in a “Total Power” computation within the maximum powercapability of the transmitter. In that event, the ACK value β_(A) is setto 1 and fed back along with the computed DRC value β_(D) to the powerand gain computation block in step 512. Conversely, if the DRC valueβ_(D) is negative, then the DRC channel is gated off by setting the DRCvalue β_(D) to 0 in step 514.

Once the DRC channel is gated off, the ACK valve β_(A) value can becomputed in step 516. The ACK value β_(A) can be computed by setting theDRC value β_(D) to 0 and solving for the ACK value β_(A) in equation(8). With the DRC value β_(D) set to 0, equation (8) can be rewrittenas:

β_(A)=(R _(M)−1−P _(T))/P _(A)  (10).

In step 518, the resultant ACK value computation is examined todetermine whether it is positive. If β_(A)≧0, then the computed ACKvalue β_(A) will reduce the ACK to pilot channel power ratio to a levelthat will result in a “Total Power” computation by the power and gaincomputation block within the maximum power capability of thetransmitter. In that event, the DRC value β_(D) is set to 0 and fed backalong with the computed ACK value β_(A) to the power and gaincomputation block in step 520. Conversely, if the ACK value β_(A) isnegative, then the ACK channel is gated off by setting the ACK valueβ_(A) to 0 in step 522.

Regardless of the back off algorithm implemented by the power throttleblock 306, the power and gain computation block 302 will compute thegains for the traffic, DRC, ACK and pilot channels once the limiter 304determines that the total reverse link transmission power is within themaximum power capability of the transmitter. Since the gains will beapplied to their respective channels in the digital domain, it isadvantageous to scale the gains to prevent an increase in the number ofbits as the gain adjusted channels are added together in the modulator.This can be accomplished by setting the gains such that the sum of theirsquares equals 1 as follows:

G _(P) ² +G _(T) ² +G _(D) ² +G _(A) ²=1  (10)

Equation (10) can be resolved as follows for each channel gain:

 G _(P)=1/{square root over (1+P _(T)+β_(D) ·P _(D)+β_(A) ·P_(A))}  (11)

G _(T) ={square root over (P_(T))}/{square root over (1+P _(T)+β_(D) ·P_(D)+β_(A) ·P _(A))}  (12)

G _(D)={square root over (β_(D) ·P _(D))}/{square root over (1+P_(T)+β_(D) ·P _(D)+β_(A) ·P _(A))}  (13)

G _(A)={square root over (β_(A) ·P _(A))}/{square root over (1+P_(T)+β_(D) ·P _(D)+β_(A) ·P _(A))}  (14)

Referring back to FIG. 3, the channel gains computed by the power andgain computation block 302 can be coupled to the modulator 210. Themodulator 210 includes a mixer 316 b which is used to spread the encodedtraffic channel from the encoder with a Walsh function. The pilot, DRCand ACK channels are also provided to mixers 316 a, 316 c, and 316 d,respectively, where they are each spread with a different Walsh cover.The Walsh covered traffic, pilot, DRC and ACK channels are provided togain elements 318 a-d, respectively, where their respective gainscomputed by the power and gain computation block 306 are applied. Theoutput of the gain elements 318 a-d are provided to a summer 320 wherethey are combined with the pilot channel. The combined channels are thencoupled to a mixer 322 where they are spread using the long PN code. Thespread channels are then split into a complex signal having an in-phase(I) component and a quadrature phase (Q) component. The complex signalis quadrature modulated with the short PN codes by mixers 324 a and 324b before being output to the transmitter portion of the RF front end204.

A complex baseband filter 326 is positioned at the input to the RF frontend 204 to reject out of band components of the quadrature modulatedsignal. The filtered complex signal is provided to quadrature mixers 328a and 328 b where it is modulated onto a carrier waveform before beingcombined by a summer 330. The combined signal is then provided to theVGA 308 to control the power of the reverse link transmission throughthe antenna. An AGC signal from the power and gain computation block 302is used to set the gain of the of the VGA 308. The AGC signal is basedon the “Total Power” computed by the power and gain computation block302 from equation (1).

Those skilled in the art will appreciate that the various illustrativelogical blocks, modules, circuits, and algorithms described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, andalgorithms have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The methods or algorithms described in connection with the embodimentsdisclosed herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method of controlling transmission power,comprising: receiving a first to second channel power ratio; adjustingthe power ratio if a combined power of a plurality of channels exceeds athreshold, the channels including the first and second channels; andcomputing gain of the first channel as a function of the power ratio. 2.The method of claim 1 further comprising applying the computed gain tothe first channel, combining the channels, and applying a second gain tothe combined channels.
 3. The method of claim 2 wherein the applicationof the second gain comprises setting power of the second channel as afunction of a criterion.
 4. The method of claim 3 wherein the criterioncomprises minimum power to achieve a quality of service at a remotesite.
 5. The method of claim 2 wherein the application of the secondgain comprises computing the second gain as a function of received powerof a transmission from a remote site.
 6. The method of claim 2 whereinthe application of the second gain comprises recovering a power commandfrom a transmission received from a remote site and computing the secondgain as a function of the recovered power command.
 7. The method ofclaim 2 further comprising spreading each channel with a different code.8. The method of claim 7 wherein the different codes each comprises aWalsh function.
 9. The method of claim 1 wherein the power ratioadjustment comprises computing the combined power of the channels as afunction of the power ratio and power for the second channel, comparingthe combined power computation to the threshold, and reducing the powerratio if the combined power computation exceeds the threshold.
 10. Themethod of claim 9 further comprising computing the power for the secondchannel as a function of a criterion.
 11. The method of claim 10 whereinthe criterion comprises minimum power to achieve a quality of service ata remote site.
 12. The method of claim 10 wherein the power computationfor the second channel comprises computing the power for the secondchannel as a function of received power of a transmission from a remotesite.
 13. The method of claim 10 wherein the power computation for thesecond channel comprises recovering a power command from a transmissionreceived from a remote site and computing the power for the secondchannel as a function of the recovered power command.
 14. The method ofclaim 9 wherein the power ratio reduction comprises reducing the powerratio in incremental steps.
 15. The method of claim 9 wherein the powerratio reduction comprises computing the power ratio reduction as afunction of the threshold.
 16. The method of claim 1 wherein thechannels further comprise a third channel, the method further comprisingreceiving a third to second channel power ratio, adjusting the third tosecond channel power ratio if the combined power of the channels exceedsthe threshold with the first to second power ratio adjusted to zero, andcomputing gain of the third channel as a function of the third to secondchannel power ratio.
 17. The method of claim 16 wherein the third tosecond channel power ratio adjustment comprises computing the combinedpower of the channels as a function of the third to second power ratiowith the first to second power ratio adjusted to zero, comparing thecombined power computation to the threshold, and reducing the third tosecond channel power ratio if the combined power computation exceeds thethreshold.
 18. The method of claim 17 wherein the third to secondchannel power ratio reduction comprises reducing the third to secondchannel power ratio in incremental steps.
 19. The method of claim 17wherein the third to second channel power ratio reduction comprisescomputing the third to second channel power ratio reduction as afunction of the threshold.
 20. The method of claim 1 further comprisingreceiving, in addition to the first to second channel power ratio, apower ratio for each remaining channel with respect to the secondchannel, and wherein the gain computation comprises dividing the squareroot of the first to second power ratio by the square root of the sum ofthe first to second channel power ratio and the power ratios for each ofthe remaining channels.
 21. The method of claim 20 further comprisingapplying the computed gain to the first channel, combining the channels,and applying a second gain to the combined channels.
 22. The method ofclaim 21 wherein the application of the second gain comprises computingthe second gain as a function of received power of a transmission from aremote site.
 23. The method of claim 21 wherein the application of thesecond gain comprises recovering a power command from a transmissionreceived from a remote site and computing the second gain as a functionof the recovered power command.
 24. Computer readable media embodying amethod of controlling transmission power, the method comprising:receiving a first to second power ratio; adjusting the power ratio if acombined power of a plurality of channels exceeds a threshold, thechannels including the first and second channels; and computing gain ofthe first channel as a function of the power ratio.
 25. Thecomputer-readable media of claim 24 wherein the power ratio adjustmentcomprises computing the combined power of the channels as a function ofthe power ratio and power for the second channel, comparing the combinedpower computation to the threshold, and reducing the power ratio if thecombined power computation exceeds the threshold.
 26. Thecomputer-readable media of claim 25 wherein the method further comprisescomputing the power for the second channel as a function of a criterion.27. The computer-readable media of claim 26 wherein the criterioncomprises minimum power to achieve a quality of service at a remotesite.
 28. The computer-readable media of claim 25 wherein the powercomputation for the second channel comprises computing the power for thesecond channel as a function of received power of a transmission from aremote site.
 29. The computer-readable media of claim 25 wherein thepower computation for the second channel comprises recovering a powercommand from a transmission received from a remote site and computingthe power of the second channel as a function of the recovered powercommand.
 30. The computer-readable media of claim 25 wherein the powerratio reduction comprises reducing the power ratio in incremental steps.31. The computer-readable media of claim 25 wherein the power ratioreduction comprises computing the power ratio reduction as a function ofthe threshold.
 32. The computer-readable media of claim 24 wherein thechannels further comprise a third channel, the method further comprisingreceiving a third to second channel power ratio, adjusting the third tosecond channel power ratio if the combined power of the channels exceedsthe threshold with the first to second power ratio adjusted to zero, andcomputing gain of the third channel as a function of the third to secondchannel power ratio.
 33. The computer-readable media of claim 32 whereinthe third to second channel power ratio adjustment comprises computingthe combined power of the channels as a function of the third to secondchannel power ratio with the first to second power ratio adjusted tozero, comparing the combined power computation to the threshold, andreducing the third to second channel power ratio if the combined powercomputation exceeds the threshold.
 34. The computer-readable media ofclaim 33 wherein the third to second channel power ratio reductioncomprises reducing the third to second channel power ratio inincremental steps.
 35. The computer-readable media of claim 33 whereinthe third to second channel power ratio reduction comprises computingthe third to second power ratio reduction as a function of thethreshold.
 36. The computer-readable media of claim 24 wherein themethod further comprises receiving, in addition to the first to secondchannel power ratio, a power ratio for each remaining channel withrespect to the second channel, and wherein the gain computationcomprises dividing the square root of the first to second channel powerratio by the square root of the sum of the first to second channel powerratio and the power ratios for each of the remaining channels.
 37. Anapparatus, comprising: a transmitter gain control configured to receivea first to second channel power ratio, adjust the power ratio if acombined power of a plurality of channels exceeds a threshold, thechannels including the first and second channels, compute gain of thefirst channel as a function of the power ratio; and a transmitterconfigured to apply the computed gain to the first channel, combine thechannels, and apply a second gain to the combined channels.
 38. Theapparatus of claim 37 wherein the transmitter gain control comprises anopen loop control configured to estimate received power of atransmission from a remote site, the second gain being computed by thetransmitter gain control as a function of the estimated received power.39. The apparatus of claim 37 further comprising a receiver configuredto receive a transmission from a remote site, the transmission having anpower command, the transmitter gain control further configured torecover the power command from the transmission received and compute thesecond gain as a function of the recovered power command.
 40. Theapparatus of claim 37 wherein the apparatus further comprising areceiver configured to receive a transmission from a remote site, thetransmission having an power command, the transmitter gain controlcomprising a closed loop control configured to recover the power commandfrom the transmission received and an open loop control configured toestimate received power of the transmission, the second gain beingcomputed by the transmitter gain control as a function of the recoveredpower command and the estimated received power.
 41. The apparatus ofclaim 40 wherein the transmitter gain control further comprising asummer configured to sum the recovered power command and the estimatedreceived power, the second gain being a function of the summed powercommand and the estimated received power.
 42. The apparatus of claim 37wherein the transmitter comprises a modulator configured to spread eachof the first and second channels with a different code before the firstand second channels are combined.
 43. The apparatus of claim 42 whereinthe different codes each comprises a Walsh function.
 44. The apparatusof claim 42 wherein the transmitter comprises a front end having avariable gain amplifier, the combined first and second channels beingprovided to the variable gain amplifier and the second gain being usedto control the gain of the variable gain amplifier.
 45. The apparatus ofclaim 37 wherein the transmitter gain control is configured to adjustthe power ratio by computing the combined power of the channels as afunction of power of the second channel and the power ratio, comparingthe combined power computation to the threshold, and reducing the powerratio if the combined power computation exceeds the threshold.
 46. Theapparatus of claim 45 wherein the transmitter gain control comprises anopen loop control configured to estimate received power of atransmission from a remote site, the power of the second channel beingcomputed by the transmitter gain control as a function of the estimatedreceived power.
 47. The apparatus of claim 45 further comprising areceiver configured to receive a transmission from a remote site, thetransmission having an power command, the transmitter gain controlfurther configured to recover the power command from the transmissionreceived and compute the power of the second channel as a function ofthe recovered power command.
 48. The apparatus of claim 45 wherein theapparatus further comprising a receiver configured to receive atransmission from a remote site, the transmission having an powercommand, the transmitter gain control comprising a closed loop controlconfigured to recover the power command from the transmission receivedand an open loop control configured to estimate received power of thetransmission, the power of the second channel being computed by thetransmitter gain control as a function of the recovered power commandand the estimated received power.
 49. The apparatus of claim 48 whereinthe transmitter gain control further comprising a summer configured tosum the recovered power command and the estimated received power, thepower of the second channel being a function of the summed power commandand the estimated received power.
 50. The apparatus of claim 45 whereinthe transmitter gain control is configured to reduce the power ratio inincremental steps.
 51. The apparatus of claim 45 wherein the transmittergain control is configured to compute the power ratio reduction as afunction of the threshold.
 52. The apparatus of claim 37 wherein thechannels further comprise a third channel, the transmitter gain controlfurther being configured to receive a third to second channel powerratio, adjust the third to second channel power ratio if the combinedpower of the channels exceeds the threshold with the first to secondpower ratio adjusted to zero, and compute gain of the third channel as afunction of the third to second channel power ratio.
 53. The apparatusof claim 52 wherein the transmitter gain control is configured to adjustthe third to second channel power ratio by computing the combined powerof the channels as a function of the third to second channel power ratiowith the first to second channel power ratio adjusted to zero, comparingthe combined power computation to the threshold, and reducing the thirdto second channel ratio if the combined power computation exceeds thethreshold.
 54. The apparatus of claim 53 wherein the transmitter gaincontrol is configured to reduce the third to second channel power ratioin incremental steps.
 55. The apparatus of claim 53 wherein thetransmitter gain control is configured to compute the third to secondchannel power ratio as a function of the threshold.
 56. The apparatus ofclaim 52 wherein the transmitter comprises a modulator configured tospread each of the first, second and third channels with a differentcode before the channels are combined.
 57. The apparatus of claim 56wherein the different codes each comprises a Walsh function.
 58. Theapparatus of claim 37 wherein the transmitter gain control is furtherconfigured to receive a power ratio for each of the channels withrespect to the second channel, and wherein the gain computationcomprises dividing the square root of the first to second channel powerratio by the square root of the sum of the power ratios for each of thechannels.
 59. The apparatus of claim 58 wherein the transmitter gaincontrol comprises an open loop control configured to estimate receivedpower of a transmission from a remote site, the second gain beingcomputed by the transmitter gain control as a function of the estimatedreceived power.
 60. The apparatus of claim 58 further comprising areceiver configured to receive a transmission from a remote site, thetransmission having an power command, the transmitter gain controlfurther configured to recover the power command from the transmissionreceived and compute the second gain as a function of the recoveredpower command.
 61. The apparatus of claim 58 wherein t the apparatusfurther comprising a receiver configured to receive a transmission froma remote site, the transmission having an power command, the transmittergain control comprising a closed loop control configured to recover thepower command from the transmission received and an open loop controlconfigured to estimate received power of the transmission, the secondgain being computed by the transmitter gain control as a function of therecovered power command and the estimated received power.
 62. Theapparatus of claim 61 wherein the transmitter gain control furthercomprising a summer configured to sum the recovered power command andthe estimated received power, the second gain being a function of thesummed power command and the estimated received power.
 63. An apparatus,comprising: means for receiving a first to second power ratio; means foradjusting the power ratio if a combined power of a plurality of channelsexceeds a threshold, the channels including the first and secondchannels; and means for computing gain of the first channel as afunction of the power ratio.
 64. The apparatus of claim 63 wherein themeans for adjusting the power ratio comprises means for computing thecombined power of the channels as a function of the power ratio andpower for the second channel, means for comparing the combined powercomputation to the threshold, and means for reducing the power ratio ifthe combined power computation exceeds the threshold.
 65. The apparatusof claim 64 further comprising means for computing the power for thesecond channel as a function of a criterion.
 66. The apparatus of claim65 wherein the criterion comprises minimum transmission power to achievea quality of service at a remote site.
 67. The apparatus of claim 64wherein the means for computing power for the second channel comprisesmeans for estimating power of a received transmission from a remotesite, the power for the second channel being computed as a function ofestimated power.
 68. The apparatus of claim 64 wherein the means forcomputing power for the second channel comprises means for recovering apower command from a transmission received from a remote site, the powerfor the second channel being computed as a function of the recoveredpower command.
 69. The apparatus of claim 64 wherein the means forreducing the power ratio reduces the power ratio in incremental steps.70. The apparatus of claim 64 wherein the means for reducing the powerratio computes the power ratio reduction as a function of the threshold.71. The apparatus of claim 24 wherein the channels further comprise athird channel, the apparatus further comprising means for receiving athird to second channel power ratio, means for adjusting the third tosecond channel power ratio if the combined power of the channels exceedsthe threshold with the first to second power ratio adjusted to zero, andmeans for computing gain of the third channel as a function of the thirdto second channel power ratio.
 72. The apparatus of claim 71 wherein themeans for adjusting the third to second channel power ration comprisesmeans for computing the combined power of the channels as a function ofthe third to second channel power ratio with the first to second powerratio adjusted to zero, means for comparing the combined powercomputation to the threshold, and means for reducing the third to secondchannel power ratio if the combined power computation exceeds thethreshold.
 73. The apparatus of claim 72 wherein the means for reducingthe third to second channel power ratio reduces the third to secondchannel power ratio in incremental steps.
 74. The apparatus of claim 72wherein the means for reducing the third to second channel power ratiocomputes the third to second power ratio reduction as a function of thethreshold.
 75. The apparatus of claim 63 further comprising, in additionto the means for receiving the first to second channel power ratio,means for receiving a power ratio for each remaining channel withrespect to the second channel, and wherein the means for computing thegain of the first channel divides the square root of the first to secondchannel power ratio by the square root of the sum of the first to secondchannel power ratio and the power ratios for each of the remainingchannels.